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Examples

GAS POOL PRESSURE DROP AND WATER SATURATION INCREASING AREAS MAPPING BASED ON THE RESULTS OF THE REPEATED GRAVITY SURVEY WITH GRAVITY LOG AFTER TEN YEARS OF PRODUCTION IN JAMSOVEY GAS FIELD WESTERN SIBERIA - 4D + 1D JOINT GRAVITY INVERSION APPROACH

Nadym-Pur, Western Siberia,
Russian Federation
Time lapse gravity survey:
1998-2008

 

Figure 1. Pressure change in Cenomanian gas pool after 10 years of production

GEOLOGICAL PROBLEM

Monitoring of waterflooding in the main gas pool - Cenomanian, Cretaceous, К1-2pk

Seismic monitoring not an option due to the absence of a seismic signal above the structure

Study of more shallow pool in Berezov Formation, Senonian, Upper Cretaceous, К2br

GEOLOGICAL RESULTS

Local areas of pressure drop by 5-6 МPa and gas-saturation change after 10 years of production were identified

Predicted location of well clusters with gas-water contact rise and pressure drop

  Predicted gas-saturated pool in Senonian formation

 
Figure 2. Dependency of Cenomanian rock density on porosity, water- and gas-saturation

Figure 3. Dependency of gas density on preassure and temperature in Cenomanian gas-saturated sandstones

Figure 4. Cross-section of 3D density model through the wells with gravity log

Figure 5. Cross-section of 3D gas-saturation model through the wells with gravity log


3D GTAVITY INVERSION WORKFLOW

Structural framework of the model was built using 2D & 3D seismic data interpretation, including target Cenomanian and Senonian horizons of Upper Cretaceous. Wells were used to define the initial 3D  density model of target Cenomanian intervals (Upper Cretaceous, K2). 3D density model was refined by joint 3D linear inversion of surface gravity field and well log gravity data with one-meter resolution in depth (Figure 6). We used surface background measurements of 1998 and measurements after a decade of production of 2008.

3D model of gas saturation (Figure 5) was built using the dependency of Cenomanian rock density on porosity and saturation (Figure 2). The dependency of real gas density on pressure and temperature was derived (Figure 3) as well as the dependency of Cenomanian gas- saturated sandstone’s density on porosity and gas saturation (Figure 2). Gas saturation decrease was detected in the marginal part of the gas pool which is associated with contour water flood within highly permeable beds (Figure 5). In the apical part of the structure, there is a zone of abnormal pressure drop (Figure 1). New gas-saturated pool was mapped in Cenonian formation of Upper Cretaceous (Figure 4).

 

Figure 6. High-resolution (1m in depth) 3D density models of gas-saturated pool by joint gravity field and gravity log inversion: background model (1998, left) and model after 10 years of  production (2008, right)

PUBLICATIONS

1.  Petrovskyy, A.P., Fedchenko, T.A., Oblekov, G.I., Polyn, I.I., Nezhdanov, A.A., Ogibenin, V.V. Optimal Complex of Geological and Geophysical Methods for Exploring Oil and Gas-Bearing Territories: The Example of the Nadym-Purovsky Oil and Gas Production Region // Theoretical and Practical Issues of Geological Interpretation of Gravitational, Magnetic, and Electric Fields. (Proceedings of the XXXVI Session of the International Seminar named after D.G. Uspensky) Kazan, January 26-31, 2009. - P. 252-255.

 

 

 
 

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